DESCRIPTION (Verbatim from the Applicant's Abstract): The hypothesis tested during Phase I was that stable isotope-labeled microspheres and neutron activation technology can be used to measure regional organ perfusion within in vivo models. We successfully proved our hypothesis and demonstrated concept feasibility. The results of our Phase I study show that blood flow values obtained from stable isotope-labeled microspheres compare favorably to values obtained from radioactive microspheres. Phase 11 will develop new products and systems to support our microsphere product-line and advance its commercial, potential. Phase 11 will develop new microsphere labels using enriched isotopes to maximize the sensitivity of the assay and to minimize the production of activation products of the element. We will also extend this work to label additional sizes of microspheres for uses in other areas of perfusion research. We will characterize label concentration and evaluate microsphere label stability over a range of conditions. In addition, Phase II will develop a novel automated Compton-suppression, coincidence-counting system that will improve the sensitivity and specificity of spectrographic analysis of complex gamma-ray spectra following neutron activation. Finally, we will design and characterize an automated sample delivery system to neutron activate large numbers of samples. Construction will be a Phase III project funded by BioPAL. PROPOSED COMMERCIAL APPLICATION: Neutron activation-based assays can simultaneously track multiple stable-isotope labeled research products within in vivo system. This ability is of high interest to the biomedical research community. No current technology can provide this level of versatility.